1. Field of the Invention
The invention relates to a method for manufacturing a DRAM cell, and more particularly to a method for manufacturing a DRAM cell used to realize a high integration of the semiconductor device by forming a stacked capacitor around a projection after manufacturing a semiconductor substrate having a projection.
2. BACKGROUND OF THE INVENTION
Generally, a DRAM cell consists of one capacitor and one transistor. That is, A DRAM cell has a MOSFET where a channel region parallel to the surface of a semiconductor substrate is formed. On the upper part of said MOSFET, a stacked capacitor is formed and connected to a source electrode of the MOSFET. On the upper part of said stacked capacitor, a bit line is formed and connected to a drain electrode of the MOSFET.
In order to realize a high integration of the DRAM cell, the area occupied by an unit cell must be reduced. However, the ability to reduce the area occupied by the capacitor to secure the required capacitance is limited. Also, the width of gate electrode can not be reduced further once it reaches a certain size because of the channel effect. It is clear that, with the structure of the conventional DRAM cell, the area occupied by the DRAM cell can be reduced only to a certain extent since a certain sized area is required when connecting a charge storage electrode or bit line onto a semiconductor substrate.
In FIG. 1, a cross-sectional view of the structure of the conventional vertical DRAM cell is given. The conventional vertical DRAM cell is made up of a p-type silicon island 122 formed on a p-type silicon substrate 121, a highly doped n-type impurity diffusion layer 116, a word line 117 that is used as a gate electrode, a gate insulator 107, and a highly doped n-type impurity diffusion layer 112. Also, a charge storage device is formed with a highly doped n-type impurity diffusion layer 112, a capacitor insulator 103, and a plate electrode 113.
However, a capacitor area of the conventional vertical DRAM cell needed to secure the required capacitance can be reduced only to a certain size and no more.